1. Field of the Invention
The present invention relates to a porous inorganic product having open cells therein and, more particularly, to a porous light weight, high strength inorganic product useful as an acoustic material or as a filter bed material and, in addition, having open cells whose wall area per unit volume is large.
2. Description of the Prior Art
The principal conventional methods of producing an inorganic member used as an acoustic material or as a filter bed material are as follows:
In the first method, a porous inorganic member is produced by adding a foaming agent or an air-entraining agent (surface active agent) to concrete, and then molding and curing the resulting mixture.
In the second method, a porous inorganic member is produced by mixing and molding an inorganic binder and organic foam particles, heating the molded mixture, and melting and removing the organic foam particles or thermally shrinking the same (U.S. Pat. No. 3,247,294).
In the first method, the porous inorganic member obtained has a number of cells of 1 mm or less in diameter and therefore contains a great number of cells therein. For this reason, the concrete layer inevitably becomes thin. In addition, these cells tend to locally gather thereby to form gaps which are relatively large in volume, irregular in shape and non-uniform. Thus the porous inorganic member obtained is low in strength and durability. Furthermore, the sound-absorbing or filtration capacity tend to considerably decrease, because the interconnecting holes are very small in sectional area and therefore liable to get clogged by dust and dirt.
In the second method, the porous inorganic member obtained has many closed cells and a relatively small number of open cells. In addition, the open cells interconnect with one another only through very narrow holes. Thus the porous inorganic member obtained in this method is very low in acoustic absorptivity and filtration capacity.